.TH g_filter 1 "Thu 26 Aug 2010" "" "GROMACS suite, VERSION 4.5"
.SH NAME
g_filter - frequency filters trajectories, useful for making smooth movies

.B VERSION 4.5
.SH SYNOPSIS
\f3g_filter\fP
.BI "\-f" " traj.xtc "
.BI "\-s" " topol.tpr "
.BI "\-n" " index.ndx "
.BI "\-ol" " lowpass.xtc "
.BI "\-oh" " highpass.xtc "
.BI "\-[no]h" ""
.BI "\-[no]version" ""
.BI "\-nice" " int "
.BI "\-b" " time "
.BI "\-e" " time "
.BI "\-dt" " time "
.BI "\-[no]w" ""
.BI "\-nf" " int "
.BI "\-[no]all" ""
.BI "\-[no]nojump" ""
.BI "\-[no]fit" ""
.SH DESCRIPTION
\&g_filter performs frequency filtering on a trajectory.
\&The filter shape is cos(pi t/A) + 1 from \-A to +A, where A is given
\&by the option \fB \-nf\fR times the time step in the input trajectory.
\&This filter reduces fluctuations with period A by 85%, with period
\&2*A by 50% and with period 3*A by 17% for low\-pass filtering.
\&Both a low\-pass and high\-pass filtered trajectory can be written.


\&Option \fB \-ol\fR writes a low\-pass filtered trajectory.
\&A frame is written every \fB nf\fR input frames.
\&This ratio of filter length and output interval ensures a good
\&suppression of aliasing of high\-frequency motion, which is useful for
\&making smooth movies. Also averages of properties which are linear
\&in the coordinates are preserved, since all input frames are weighted
\&equally in the output.
\&When all frames are needed, use the \fB \-all\fR option.


\&Option \fB \-oh\fR writes a high\-pass filtered trajectory.
\&The high\-pass filtered coordinates are added to the coordinates
\&from the structure file. When using high\-pass filtering use \fB \-fit\fR
\&or make sure you use a trajectory which has been fitted on
\&the coordinates in the structure file.
.SH FILES
.BI "\-f" " traj.xtc" 
.B Input
 Trajectory: xtc trr trj gro g96 pdb cpt 

.BI "\-s" " topol.tpr" 
.B Input, Opt.
 Structure+mass(db): tpr tpb tpa gro g96 pdb 

.BI "\-n" " index.ndx" 
.B Input, Opt.
 Index file 

.BI "\-ol" " lowpass.xtc" 
.B Output, Opt.
 Trajectory: xtc trr trj gro g96 pdb 

.BI "\-oh" " highpass.xtc" 
.B Output, Opt.
 Trajectory: xtc trr trj gro g96 pdb 

.SH OTHER OPTIONS
.BI "\-[no]h"  "no    "
 Print help info and quit

.BI "\-[no]version"  "no    "
 Print version info and quit

.BI "\-nice"  " int" " 19" 
 Set the nicelevel

.BI "\-b"  " time" " 0     " 
 First frame (ps) to read from trajectory

.BI "\-e"  " time" " 0     " 
 Last frame (ps) to read from trajectory

.BI "\-dt"  " time" " 0     " 
 Only use frame when t MOD dt = first time (ps)

.BI "\-[no]w"  "no    "
 View output xvg, xpm, eps and pdb files

.BI "\-nf"  " int" " 10" 
 Sets the filter length as well as the output interval for low\-pass filtering

.BI "\-[no]all"  "no    "
 Write all low\-pass filtered frames

.BI "\-[no]nojump"  "yes   "
 Remove jumps of atoms across the box

.BI "\-[no]fit"  "no    "
 Fit all frames to a reference structure

.SH SEE ALSO
.BR gromacs(7)

More information about \fBGROMACS\fR is available at <\fIhttp://www.gromacs.org/\fR>.
